NaCl is fcc lattice , where `Na^+` ions are at corner and face centre position . Chloride ions are at edge centres and body centre positions.
How many NaCl formula units will be in an unit cell ?

Options

A. 2
B. 4
C. 3
D. 1

Answer

B

Explanation

NaCl has fcc lattice structure, thus it has `Na^+` ions corners and face center
`=3+1=4Na^+` units
`Cl^-`-ions are at edge center and at body center,
`3+1=4Cl^-` units.
Hence, 4 units of `Na^+` and 4 units of `Cl^-` ions give 4 units of `NA^+Cl^-`.
Hence, option (b) is the correct answer.